Density-functional calculations are used to investigate hydrogen diffusion in the solid-state proton conductor BaZr O3. Activation energies and prefactors for the rate of proton transfer and reorientation are evaluated for a defect-free region of this simple cubic perovskite-structured oxide. Both semiclassical over-barrier jumps and phonon-assisted tunneling transitions between sites are considered. It is found that the classical barriers for the elementary transfer and reorientation steps are both of the order of 0.2 eV. The quantum-mechanical zero-point motion effects are found to be sizable, to effectively reduce the barrier heights, and to make the prefactors similar for the transfer and reorientation steps. The Flynn-Stoneham model of phonon-assisted tunneling yields an activation energy of around 0.2 eV and a very small prefactor for proton transfer, whereas the corresponding adiabatic model gives a similar activation energy but a much larger prefactor. It is suggested that the effect of other defects such as dopants has to be included for a proper description of hydrogen diffusion in this material.
|Número de artículo||094301|
|Publicación||Physical Review B - Condensed Matter and Materials Physics|
|Estado||Publicada - 27 sep 2007|
Áreas temáticas de ASJC Scopus
- Física de la materia condensada
- Materiales electrónicos, ópticos y magnéticos